Recently, various types of digital appliances (such as optical disk recorders and camcorders) that can write and store content's digital data on a number of types of media including an optical disk such as a DVD, a magnetic disk such as a hard disk, and a semiconductor memory, have become more and more popular. The content may be a broadcast program or the video and audio that have been captured with a camcorder, for example.
Also, lately PCs often have the functions of recording, playing and editing a content, and may also be counted among those digital appliances. In writing data such as document data, PCs have used various media such as a hard disk, an optical disk and a semiconductor memory. That is why a file system that has a data management structure compatible with a PC such as a file allocation table (FAT) has been adopted in such media. The FAT 32 file system that is often adopted currently can handle a file that may have a maximum size of 4 gigabytes or can manage a medium with a maximum storage capacity of 2 terabytes.
The bigger the maximum storage capacity of a medium, the longer the overall playback duration of the content stored there. The optical disks, hard disks, semiconductor memories and so on are so-called “randomly accessible” media. Therefore, when a content data stream with a long duration is stored on such a medium, it would be convenient if playback could be started from any arbitrary point of the content. For example, Patent Document No. 1 generates time map information, defining correspondence between a playback time and the address at which the AV data to play back at the time is stored, at regular time intervals from the beginning of a data stream. If the start time and end time, specified by the user, are converted into a start address and an end address, respectively, by reference to the time map information and if the data stored at those addresses are read, the content can start being played back at the specified time.    Patent Document No. 1: Japanese Patent Application Laid-Open Publication No. 11-155130